package hznu.grade15x.utils;

/*
 * 此为工具类，网上搜的Base32 字符编码 解码
 * 其作用大概是丢进一个字符串 出来另一个 加密过的字符串 （通过什么复杂的位运算，具体请百度）
 */
public class Base32 {  
    
    private static final char[] ALPHABET = {  
            'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H',  
            'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P',  
            'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X',  
            'Y', 'Z', '2', '3', '4', '5', '6', '7'  
    };  
      
    private static final byte[] DECODE_TABLE;  
      
    static {  
        DECODE_TABLE = new byte[128];  
          
        for (int i = 0; i < DECODE_TABLE.length; i++) {  
            DECODE_TABLE[i] = (byte)0xFF;  
        }  
        for (int i = 0; i < ALPHABET.length; i++) {  
            DECODE_TABLE[(int)ALPHABET[i]] = (byte)i;  
            if (i < 24) {  
                DECODE_TABLE[(int)Character.toLowerCase(ALPHABET[i])] = (byte)i;  
            }  
        }  
    }  
  
    //编码
    public static String encode(byte[] data) {  
          
        char[] chars = new char[((data.length * 8) / 5) + ((data.length % 5) != 0 ? 1 : 0)];  
          
        for (int i = 0, j = 0, index = 0; i < chars.length; i++) {  
            if (index > 3) {  
                int b = data[j] & (0xFF >> index);  
                index = (index + 5) % 8;  
                b <<= index;  
                if (j < data.length - 1) {  
                    b |= (data[j + 1] & 0xFF) >> (8 - index);  
                }  
                chars[i] = ALPHABET[b];  
                j++;  
            } else {  
                chars[i] = ALPHABET[((data[j] >> (8 - (index + 5))) & 0x1F)];  
                index = (index + 5) % 8;  
                if (index == 0) {  
                    j++;  
                }  
            }  
        }  
          
        return new String(chars);  
    }  
  
    //解码
    public static byte[] decode(String s) throws Exception {  
          
        char[] stringData = s.toCharArray();  
        byte[] data = new byte[(stringData.length * 5) / 8];  
          
        for (int i = 0, j = 0, index = 0; i < stringData.length; i++) {  
            int val;  
              
            try {  
                val = DECODE_TABLE[stringData[i]];  
            } catch (ArrayIndexOutOfBoundsException e) {  
                throw new Exception("Illegal character");  
            }  
              
            if (val == 0xFF) {  
                throw new Exception("Illegal character");  
            }  
              
            if (index <= 3) {  
                index = (index + 5) % 8;  
                if (index == 0) {  
                    data[j++] |= val;  
                }  
                else {  
                    data[j] |= val << (8 - index);  
                }  
            } else {  
                index = (index + 5) % 8;  
                data[j++] |= (val >> index);  
                if (j < data.length) {  
                    data[j] |= val << (8 - index);  
                }  
            }  
        }  
          
        return data;  
    }  
}  
